In known wood processing machines used to convert logs into chips or flakes, it has been common for the machines to include one or more knives mounted either on the face of a rotary disc or on the circumferential surface of a rotating drum. The logs are guided or urged into the disc or drum so that the knives cut away chips or flakes of wood as the log is consumed by the knives. It is preferable to orient the log at an angle of 38 degrees with respect to the path of travel of the knives through the wood in order to minimize the power required to drive the knives across the grain of the wood.
The knives conventionally utilized in such known wood processing machines generally have a linear cutting edge formed by double grinding a metal blank to form a sharp edge between the back surface of the knife and an end (gullet) face. The cutting edges of such knives are typically two inches or more in length, and also can include wings as shown in U.S. Pat. No. 3,219,076 and No. 3,559,705. As the sharp cutting edge of a knife dulls, the knife loses the heal clearance provided between the back surface of the knife and the surface of the wood. In order to permit penetration of the sharp edge into the wood, a heel clearance angle of about two to eight degrees between the back surface of the knife and the wood should be provided. When the knife edge dulls, the heel clearance adjacent to the cutting edge disappears, and the knife tends to drag along the wood rather than penetrating into the wood. This causes the knife to dull even more quickly. More power is then required to drive the dull knife through the wood and significant resources must be utilized to change the knives and to resharpen the dull knives. Downtime of the wood processing machine is directly related to the frequency of the intervals at which the knives must be changed. Also, good penetration is required in order to cut thin flakes of wood, and therefore conventional knives that dull quickly cannot be used for continuous cutting of thin flakes.
In some known wood processing knives, a single elongated metal blank is formed into sections, as is shown in U.S. Pat. No. 2,997,082. In such patent, sharpened working edge sections which are about 11/8" in length are separated by 7/8" non-cutting recesses. Adjacent rows of such multiple knives are staggered on a drum so that the working segments overlap as the drum rotates. In U.S. Pat. No. 2,951,518, a wood processing knife is shown in which grooves have been machined in the end (gullet) face of the knife to at least the depth of cut in order to divide the wood flake being removed from the log into separate narrow ribbons. U.S. Pat. No. 2,349,034 shows a shreading cutter which includes triangular teeth formed by grooves in the back surface of the cutter. The cutter is drawn with the grain of the wood to scratch out "wood wool" shreads or filaments. U.S. Pat. No. 2,813,557 shows a knife including a plurality of spaced forward blade edges and a plurality of integral rear wood blade edges disposed between the forward blade portions. The serrated forward blade edge is formed by grooves in the gullet face of the knife such that the size of chips is determined by the spacing between the forward teeth. It appears that the depth of cut is less than the depth of the grooves. In U.S. Pat. No. 2,825,371, chip breaking teeth 32 are spaced apart along the gullet surface of the cutting knife, the edge of which is a conventional continuous linear cutting edge. Other knife configurations in various types of wood processing machines are shown in U.S. Pat. Nos. 3,732,907; 3,304,970; 242,138; 3,011,535; 2,964,079; 4,077,450; 3,327,746; 3,907,016; 3,421,561; 3,262,476; 3,162,222; 3,059,676; 2,997,082; 2,710,635; 3,219,076; 3,559,705; and 3,195,592.
A need has existed in the wood processing art for a knife that can retain its sharpness for longer periods of time and thereby be capable of precision cutting very thin flakes from the ends of logs.